1. Field of the Invention
The present invention relates to a blower. More particularly, the present invention relates to a blower used for circulating a laser medium in a laser oscillator, in which gas is used as the laser medium, such as a chemical laser or a gas laser.
2. Description of the Related Art
A gas laser, especially a carbon dioxide gas laser is used for cutting and welding a metal material or a nonmetal material. In the case of a gas laser oscillator, a laser medium, for example, carbon dioxide gas is circulated between an electric discharge tube and a heat exchanger, which is a laser medium cooling device, so as to maintain a temperature of carbon dioxide gas at an appropriate value. In order to circulate the laser medium, a centrifugal blower, an example of which is shown in FIGS. 4a and 4b, is usually used.
In FIGS. 4a and 4b, the blower 50 of the prior art includes a blade 54, which is pivotally supported by a drive motor 56 so that the blade 54 can be freely rotated round a central axis O by the drive motor 56, wherein this blower 50 is arranged in a casing 52 in which a suction port 52a and an exhaust port 52b are defined. In order to rotate the blade 54, a space G is provided between the blade 54 and the casing 52. In the blower 50 of the prior art, a gap formed between the blade 54 and the casing 52 is constant all over the region of the space G. Accordingly, concerning the interval Gi formed in a region adjacent to the suction port 52a and the interval Go formed in a region adjacent to the exhaust port 52b, while consideration is being given to the blower efficiency and reliability, the intervals Gi and Go are determined at the same value and in a range from 0.1 mm to 1.0 mm.
In the blower used for a laser oscillator, in the case where the accuracy of rotation is deteriorated due to the abrasion caused in bearings 58a, 58b, the blade 54 comes into contact with the casing 52. At this time, a minute dust is generated in the casing 52 and mixed into the laser medium. When this dust contained in the laser medium attaches to a mirror, the laser output is lowered. Accordingly, it is necessary to maintain a laser medium passage clean at all times. Therefore, it is necessary to prevent the blower blade 54, which is used for circulating the laser medium, from coming into contact with the casing 52. In order to accomplish the above object, it is desirable to extend a space G formed between the blade 54 and the casing 52. However, when the space G formed between the blade 54 and the casing 52 is extended, the blower efficiency is deteriorated. On the other hand, in order to realize a high blower efficiency, it is effective to reduce the space G formed between the blade 54 and the casing 52 so as to decrease a leakage of fluid from the space. However, when the space G is reduced, there is a high possibility that the blade 54 comes into contact with the casing 52. Therefore, the reliability of the blower is lowered.
It is the technical task of the present invention to solve the above problems of the prior art. An object of the present invention is to provide a highly reliable blower used for a laser oscillator, the deterioration of the blower efficiency of which is minimized.